In recent years, there has been an increasing trend toward higher image quality with the marked improvement in the image quality offered by silver halide color photographic light-sensitive materials.
Meantime, since the development of photographic processing systems of relatively small scale known as mini-laboratories, there have been increasing cases where photographic materials are processed at retail shops such as photo shops. These small-scale processing laboratories undergo more difficulties in processing management than do large-scale processing laboratories. Accordingly, there is a need for the development of color photographic light-sensitive materials of reduced processing variability.
With respect to such processing variability, attempts have been made to improve processing solutions to increase processing stability, but no satisfactory effects have been obtained. From the viewpoint of improvement of silver halide color photographic light-sensitive materials, some methods have been proposed which are based on the concept of equalizing the developing speeds in respective emulsion layers.
For example, to equalize the developability of silver halide grains in a layer of higher sensitivity to that in a layer of lower sensitivity within the same spectral sensitivity, the grain size of silver halide grains in the layer of higher sensitivity is decreased, or a layer of relatively low silver iodide content or a layer having an appropriate silver chloride content is formed on the surface of the grains. However, grain size reduction or change in a halide content results in a loss of sensitivity and deterioration of granularity. Also, silver iodide content reduction generally results in deteriorated color reproduction because IIE decreases.
Also, it is a well-known approach to improvement in color reproduction to add a DIR compound to the color light-sensitive material. However, this method has a drawback that increasing the amount of addition results in significant loss of sensitivity or color reproducibility. Another drawback is that processing stability is deteriorated as a result of accumulation of the developing inhibitor released in the processing solution.
The same tendency, though varying in degree, was seen even when using a DIR compound which loses its suppressive action upon release in the developer.
In these circumstances, the present inventors concluded that silver halide grains themselves should be improved to obtain a color light-sensitive material having suppressed processing variability and high IIE (Inter-image effect) while maintaining a good balance between sensitivity and granularity.
The present inventors first marked emulsions of tabular grains of high aspect ratio, which offer relatively high developing speed and are therefore advantageous form the viewpoint of sensitivity. The inventors prepared emulsions comprising grains whose silver halide composition is varied therein to increase IIE, i.e., emulsions based on a combination of tabular twin crystal grain technology and core-shell grain technology as described in Japanese Patent Examined Publication No. 38692/1988 and Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 14636/1986, and tabular twin crystal emulsions wherein a layer of relatively high silver iodide content is formed on the grain surface as described in Japanese Patent O.P.I. Publication No. 284848/1989, and compared their photographic performances. Although IIE improved, granularity deteriorated significantly probably because of the wider grain size distribution than in normal crystal emulsions, with almost no improvement in processing variability.
With this in mind, the inventors prepared a monodispersed emulsion of low aspect ratio having two mutually parallel twin crystal planes, as described in Japanese Patent O.P.I. Publication No. 163433/1991, and evaluated its photographic performance in each of the emulsion layers of the same spectral sensitivity. Although processing variability was successfully improved without deterioration of sensitivity or granularity, no sufficient IIE was obtained.
The present inventors then studied to improve IIE alone in such a monodispersed emulsion comprising grains of low aspect ratio having two mutually parallel twin crystal planes, and found that the essential object can be accomplished when each of the emulsion grains has a development starting point near the intersection of a line formed by a twin crystal plane exposed to the grain surface and a edge of the grain.